How can I declare global variables then I can access them on the other forms?

And how can I use radio button for choose statement? thanks. .

If you declare a (global) variable in your main form:

Public Class Form1

  Friend MyGlobal As Integer

End Class

you'll have to qualify variable's name with Form1

Public Class Form2

  Dim a As Integer = Form1.MyGlobal

End Class

And how can I use radio button for choose statement?

You mean, how to test the value? Use Checked property:

If RadioButton1.Checked Then
  ' Radio button is "checked"
End If